Petroleum-based plastic foam materials, such as Styrofoam, polyurethane foam, and phenolic foam have been used for thermal insulation of commercial and industrial building structures. However, such foams exhibit limited fire resistance even after fire-retardant treatments. When exposed to high temperature flame, plastic foams undergo repaid thermal degradation and decomposition along with the emission of hazardous fumes and smoke.
Fiberglass and mineral wool insulations have found extensive application for residential housing in North America. These inorganic fibers offer better fire protection than petroleum-based foams. But flexibility and “fluffy” nature of such fiber insulations make them hard to retain fasteners, bolts and any other hardware resulting in more difficult and expensive construction and installation for applications, such as exterior wall insulation.
There has been a long-recognized need for rigid thermal insulation materials with good fire resistance and mechanical strength. U.S. Pat. No. 4,240,839 to Crepeau et al. discloses an insulating assembly comprising a low density foamed gypsum material and entrainment air. This gypsum foam has been further reinforced with cement and mineral wool as described in U.S. Pat. No. 4,310,996 to Mulvey et al. But mechanical strength of such foamed gypsum is still unsatisfactory and it needs to be protected by structural surface elements.
U.S. Pat. No. 4,265,964 to Burkhart points out that entrainment of air alone will not create a gypsum wallboard with sufficiently low density, and meanwhile, maintain adequate strength. Among ingredients for lightweight gypsum compositions disclosed in this patent, thermoplastic granules have been introduced to balance lightweight requirement and strength reduction. A rubbery polymeric latex is also used for adding strength, integrity and flexibility to the final gypsum structural units. U.S. Pat. No. 6,602,924 to Chiang et al. discloses a foamed gypsum formulation containing mainly gypsum, foaming agents, epoxy resin and a hardener.
U.S. Pat. No. 3,989,534 to Plunguian et al. discloses a cellular product comprised of mineral cement, a film former, surfactants, lightweight aggregates, and excessive amount of air. U.S. Pat. No. 4,303,450 to Hacker discloses a sprayable insulation composition containing Portland cement, lime, diatomite and a water-soluble foaming agent. U.S. Pat. No. 5,529,624 to Riegler describes a fire retardant insulation material produced from a perlite and zeolite mixture bound together by cement and lime without an air-entraining or foaming process.
Foamed gypsum materials, compared to foamed cement, offer advantages of fast setting, early hardening, high early strength, and better fire protection and thermal insulation abilities. However, gypsum is sensitive to water and limited to interior applications if without any waterproofing treatment. On the other hand, foamed cement demonstrates good water resistance, environmental durability and strong mechanical strength, but also exhibits a long set time which results in long lead time. This could be a significant disadvantage and have a negative impact on productivity and capacity, especially when there are further processing steps needed to be done after cement hardening and setting.
Adding a large percentage of calcined gypsum (calcium sulfate hemihydrates) into Portland cement is usually unfeasible because of the formation of ettringite and thaumasite, which may cause expansion and performance deterioration. Some “pozzolanic” materials, such as silica fume, metakaolin, and furnace slag et al., have been tried in gypsum-cement systems to prevent the deleterious effect of ettringite and thaumasite. Pozzolanic activities of silica fume have been discussed by Kovler in his article published in Cement and Concrete Research, Vol. 28, No. 3, pp. 423-437, 1998. U.S. Pat. No. 6,241,815 to Bonen discloses a gypsum-cement system with good water durability, which contains pozzolanic materials to minimize the formation of ettringite and thaumasite. U.S. Pat. No. 5,401,538 to Perito discloses sprayable cement-based fireproofing compositions mainly comprised of Portland cement, a high density aggregate, gypsum stucco, a stucco set retarder and shredded polystyrene aggregate. Densities of the resulted materials are quite high. U.S. Pat. No. 6,290,769 to Carkner discloses a lightweight insulating mixture of Portland cement, plaster of Paris (calcium sulfate hemihydrates), terra alba (calcium sulfate dihydrate) and lightweight aggregates. Above prior-art patents have explored opportunities to combine the advantages of both gypsum and cement. However, none of them has also focused on achieving good thermal insulating properties and energy efficiency.
Phase change materials (PCM) have drawn a lot of interest from architectural and building industries where energy consumption for indoor climate control is becoming one of the major considerations for residential and commercial building design and operation. A phase change material utilizes latent heat of fusion for thermal storage at its melting/freezing point. During solid-liquid phase transitions, phase change materials absorb and release large amounts of heat energy without a change in temperature. Based on this unique function, phase change materials can be incorporated into building component to assist in maintaining interior temperature within a comfort range and saving gas or electrical energy. For example, in summer months, building elements containing phase change materials absorb solar energy and prevent solar heat from directly penetrating into the interior of a room. As a result, the interior temperature can be kept cool for a longer time and the workloads of air conditioning system can be alleviated. In winter months, the phase change materials stop the interior heat generated by indoor heaters or a house furnace dispersing into the cold exterior environment. They absorb and store the heat energy through solid to liquid phase transition, then, release the energy back to the interior when the room temperature drops below their inching points, which leads to a significant reduction in electricity and natural gas consumption.
U.S. Pat. No. 4,587,279 and U.S. Pat. No. 4,797,160 to Salyer et al. disclose cementitious building materials directly incorporated with phase change materials. Later, U.S. Pat. No. 5,755,216 to Salyer points out that direct adding phase change materials into cementitious compositions can cause significant reductions in mechanical strength of the final products. In order to avoid this negative impact, phase change materials have been impregnated into finished building products after manufacturing. U.S. Pat. No. 4,988,543 to Houle et al. discloses a method and an apparatus for spraying a phase change material on one side of gypsum wallboards. The impregnation of phase change materials into porous products can be enhanced by exposure to microwave energy as described in U.S. Pat. No. 5,202,150 to Benson et al. However, post-manufacturing impregnation creates building products with high surface phase change material concentrations. Because most phase change materials are flammable, impregnated products need extra flame retardant treatments. U.S. Pat. No. 5,788,912 to Salyer discloses a method of treating porous product surfaces containing phase change materials with a urea fire-retarding agent. U.S. Pat. No. 5,755,216 to Salyer discloses a method of inserting phase change material-containing composites into hollow cores of cementitious building blocks. In addition, unencapsulated phase change materials, when in liquid state, could flow away from their original positions, so it is better to seal them inside of small capsules before being added into the cementitious matrix. U.S. Pat. No. 4,747,240 to Walter et al. discloses phase change capsules incorporated into building materials like a fine aggregate. U.S. Pat. No. 7,166,355 to Jahns et al. teaches the use of microencapsulated phase change materials in gypsum plasterboard compositions.